A spin-transfer torque memory (STTM) is a type of magnetoresistive memory that can employ a magnetic tunnel junction (MTJ) device. A typical MTJ device configuration includes an oxide-based tunnel barrier layer sandwiched between a fixed magnetic layer and a free magnetic layer. The direction of magnetization in the fixed layer is normally maintained as a reference, and the direction of magnetization in the free layer is adjusted relative thereto. When the MTJ device is in its low resistivity state—that is, the directions of magnetization for the fixed and free layers are parallel with one another—electrons with spins oriented parallel to the magnetization (spin-up electrons) readily pass from the fixed magnetic layer through the tunnel barrier layer to the free magnetic layer, and electrons with spins oriented anti-parallel to the magnetization (spin-down electrons) are strongly scattered. Contrariwise, when the MTJ device is in its high resistivity state—that is, the directions of magnetization for the fixed and free layers are anti-parallel with one another—electrons of both types of spins (spin-up and spin-down electrons) are strongly scattered, and quantum tunneling through the tunnel barrier layer is suppressed. Thus, a STTM employing a MTJ device can be considered a programmable magnetoresistive memory, wherein a binary ‘0’ can be stored in the MTJ device by changing its resistance to the low resistivity state and a binary ‘1’ can be stored by changing its resistance to the high resistivity state. Within the context of a STTM, the free magnetic layer's direction of magnetization can be switched through spin-torque transfer using a spin-polarized current.
These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Furthermore, as will be appreciated, the figures are not necessarily drawn to scale or intended to limit the described embodiments to the specific configurations shown. For instance, while some figures generally indicate straight lines, right angles, and smooth surfaces, an actual implementation of the disclosed techniques may have less than perfect straight lines, right angles, etc., and some features may have surface topology or otherwise be non-smooth, given real world limitations of fabrication processes. In short, the figures are provided merely to show example structures.